Lighting the way

Achieving consistent and reliable street and open air lighting in areas of the world without a grid system is a considerable challenge and especially so in extreme climatic conditions. Yet the benefits in terms of safety and security for citizens, are immense.

Sunna Design, a French designer and manufacturer of solar lighting, is tackling this problem with a range of lighting solutions adapted for rural, arid or desert regions where installation and on-going maintenance are difficult. Sunna has developed lamp posts topped with solar panels which are equipped with a nickel-metal hydride (NiMH) battery, coupled with a smart energy management system. The lamps provide public lighting in remote areas which is essentially maintenance free, designed to limit vandalism and quick and simple to install.

For stand-alone solar lighting systems, a light weight battery can be an important advantage when set at height. Small NiMH batteries are integrated inside the head of the lamp and placed at the top of a mast. This significantly simplifies installation and avoids both having to bury the battery in the ground, as well as the need for cabinets or external electrical connections.

Durable battery chemistry

To ensure that the battery has a long life, charge and discharge management is the key element. End-of-charge and end-of-discharge detection methods are used to prevent over-charge and over-discharge, and are programmed into the battery management system.

The choice of a nickel-based battery was the result of a two year study with French research laboratory, CEA-INES, part of the National Institute for Solar Energy. The researchers compared battery technologies which can be used in extreme conditions. “Rainfall, solar radiation and intense heat as well as sand storms and desert winds of up to 100km/h all had to be taken into account,” explains Raphael Baillot, Head of R&D for Sunna. Air temperature is the most sensitive environmental factor for a battery and the objective was to find the most resistant battery chemistry for desert environments, and improve its performance and lifespan in tough conditions.

Unrivalled lifespan

Accelerated aging tests confirmed NiMH technology for its efficiency and predicted a lifespan of ten years as well as suitability for Africa or Middle East desert operating conditions. Here temperatures can range from around 58°C during the day to 10°C at night, and in some regions at certain times of the year can even fall to around freezing. The battery therefore needs to function reliably over a wide temperature range. “The nickel-based batteries allow us to reach an unrivalled lifespan for our products,” says Baillot.

The high temperature resistance of this metal allows us to get an optimum performance even under the harshest environments on earth,” says Sunna engineer, Nicolas Mercadal. “This is the best battery technology for solar lighting applications.”

“Because the battery stores solar energy during the day for use at night, efficiency of the system’s energy storage is critical. In African countries, lead acid batteries in similar systems have a life of up to two years and can expire in less than a year. “Reliability provided by NiMH batteries prevents additional maintenance costs,” says Laura Pargade, Sunna’s Head of Marketing. “A smart electronic energy management system optimizes the lighting program whatever the weather and enhances the battery lifespan.” NiMH offers reasonable specific energy (55 to 70 Wh/kg) and covers one of the largest temperature ranges available for rechargeable battery technologies, from -20 to + 70°C.

Communities in over 20 countries are now benefiting from the systems. Many are in Africa, including Senegal, Nigeria and Cameroon, as well as a refugee camp in Jordan.

Blackouts in remote areas could be a thing of the past thanks to solar lighting systems based on NiMH battery technology with the potential to bring light to everyone, everywhere, reliably and sustainably.

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Ziguinchor is the chief town of the Casamance area of Senegal and has a population of over 230,000. It lies at the mouth of the Casamance River and has a bustling harbour, with areas dedicated to the fishing industry where locally caught fish are smoked and sold. Before the municipality installed the Sunna Design solar street-light “Maxi” system, the fishermen attached flashlights to their heads with tape to enable them to work in the dark. Selling fish when the fishing boats arrived at the dockside was restricted because of the darkness but now, with the aid of the solar street lights, commercial activities which start there at 4 a.m. are being developed.

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